Multizone air conditioning system



June 20, 1944 A. B, NEWTON MULTIZONE AIR CONDITIONING SYSTEM 2Sheets-Sheet 1 Filed April 17, 1942 I INVENTOR. Alwin 13. New-10mAHorney- I he; present invention is directed broadly to an anisoInaticcontrol system for air conditioning a plnrality of zones, and ismore particularly di rected to a system in which the air in these zonesis cooledby a direct expansion refrigeration systein which is fed by ,avariable capacity conipre orfarrangement in which the capacity is variedin accordance with the demand for cooling'by the several zones;

,Qne of the principal objects of this invention is gt o providethermostatic means for measuring the-:total load ontthe entire system.and, to prevent operationi of the compressor means until of'Fthefinaximum load, this percentage being such that thecompressor meansmay operate efiicient lyfat minimum capacitywithout short cycling.Tfiejinvntion further contemplates increasing the capacity of thecompressor means as the load on, the system increases "to ,a' maximum.

Th "comm s'stem len s itself to the control offaplurality of zones'qr's'pa'cejswherein the 'vari-' "spaces represent "dif fefrent'loads onthe sys tem fElectrical neans f are provided for controlling thevariable capacity compressor means and me electrical mean'si'areaffected by the temperatureresponsive means'in the "various spaces inseeprdaneewitntm load which that particular s ace represents." i

;further-' object of the invention is to make electrical-device in theform of a proportioni'n'g 'motor having a control potentiometer in whichvariable portions ofthe control potentiometer are-shunted bythermostatic means in the spacestobe conditioned. I 1

wstill another object of the invention is to make the' eiectricalxdevice in the form of a plurality of current-responsive:relays, thecurrent through theseirelays being varied by thermostatic deviceslocatedin thespaces; to be'conclitioned. I?

'1hese-and other objectswill rea'dily'become apparentas thefollowingspecification isread in thelightof the accompanying drawings, in whichdFigure 1 i s:a;diagrammatic illustration of :a controlsystem embodyingthe various features ot gnytinvention, 1 1 Figure 2 is a. view showingamodified form of thermostatic control device which may be utiliked in"the various spaces, and v j Figure '3 is a diagrammatic representationof a rnodified form of my invention. v I v iInflFigure 1} of thedrawings a building l0, iv iclitmay be aj'col'd storage building-, isshown secticnally'in plan view and comprises six zones or cold storager'oomsas indicated at A, B, C, D,

itgisquite'usual to maintain the various rooms at difierenttemperaturesand these rooms are also usu llyr; difiere'nt sizes! ,Ittherefore v follows thatieachiof ith'ese rooms r'epre'sentS "a: mfiflfen't percentage of" the total "load "on the -enti'rl'a sys' th loadreach'es a certain definite percentage S TES jf' 'ivrct'rlzohfn SY EM?Alwin B. Newton} Minneapolis, Minn; assig nor I to Minneapolis-HoneywellRe'gulatonCompany,; L 4; Minneapolis, Minn, a corporation f Delaware vApplication strait, ministerial Qatar 10 Claims.

Merely by, way of example, let'it be"ass'umed thatroom A' is to be'maintain'ed at 55, Bat 45, C at 40, D at E at 35 andF at Also, let it'be assumed that room A represents 20%fof the total load on; the entiresystem B 15%, 05%, D 15%, E 15% and F30%. Itis obvious that aproperfcontrol, would not be etfj fected by permitting the temperaturein eachof these spaces to; have an equal effect upon the capacity on thecompressor'means The purpose of this invention therefore, 'is tocorrelate the controls for the various spaces so-that each will affectthe ca 'Jacityofv the. system in accordance with thepercent'age oftotal'loa'd 'on the system whichitrepresents H v lilach of these spacesis provided with I an evaporator and control unit therefor as shown atHaj, lib, He, ltd, i le, and i If.- These units are of a size dependingupon which space they are in; and they are underthe control pr,individual spacethermostats as shown at l 2a, I21), I20, 12d, He' and12f. I Inasmuch as allof the control units and thermostats therefor arethe same for each, space, only one of .these;units will be described intdetail. This unit is shown as lld in the spaceD. u v I Unit I id isshownascomprising an air conditioning chamberii through which space airmay be circulated vbyv m ans of a fan not shown. The chamber lii isprovided with a partition [6 which forms in ei'fect aYfirst-conduit inwhich the refrig'er'ant evaporator His located and a second by-pass'conduit l8. vThe relative proportions of air flowing across theevaporatorfand through the 'by-pas's is controlled by means of thesplitter damper is The splitter damper l9is controlled bymeans of, theelectric proportioning motor 20 which in turn is positioned by, the-space thermostat l2d which moves the slider 2|v over the resistance 22in' accordance with the, temperature in the jspace Dg Th ef arrangementis such that the damperls; under, the influence of the motor 20;; willtake'a position corresponding to the positionof theslider zi on theresistance'22. Proportioning systems of thistype are well known in theprior art andfif desired may take'the form Ef'and F." Incoldstoragebuildings of this type shown'in thepatent'ftoT'D. G., Taylor, 2,028,110which issuedv January 14, 1936. The electrical circuits are so arrangedthatwhen the temperature in the space D is relatively' low the slider 2|'vwill'taketa' position at the right hand end or the resistance 22and'the splitter damper l9 will therefore cause substantially all of theair to by-' pass the"ev'aporator H, The slider 2! will be moved to theleftacross the resistance 22 as the temperature in the space increasesand the damper 19 will therefore move correspondingly toward the left tocause more'and more of the air from the'sfpace to: pass over the"evaporator 19 .l 'prb ortioningmotor through its crank arm 23', isadapted also to actuate the mercury switch in such a manner that whenthe slider arm 2| is, at the right hand end of the resistance 22 thecrank arm 23 will be in a position to maintain the mercury switch 25 inopen circuit position, but as soon as the slider arm 2| moves slightlytoward the left from its right hand position, the crank arm 23 will movemercury switch 25 to closed circuit position. The mercury switch 25controls a circuit throughconductors :26, 21 and 28 to the electricallyoperated'valve 29 located in the inlet to the evaporator As long theevaporator in the event that the temperature in the space issufficiently low and for permitting such flow when there is a demand forcooling in the space. Also, each of the evaporators is provided with theusual expansion valve 65 for @maintaining a constant degree of superheatat as the temperature in the space D is relatively low and the sliderarm 2| has moved to its right hand position wherein the splitter damperI9 is causing substantially all of the air to by-passthe evaporator N,there is no need for the evaporator to be in operation so under theseconditions the mercury switch 25 is in open circuit position and theValve 29 in the'inlet to the evaporator is closed. However, as soon asthere is need for cooling in the space D as indicated by the movement ofthe slider arm 2|' toward the left on the resistance 22, the splitterdamper l9 will be moved toward the left to permit a certain amount ofair to fiow' across the evaporator l1 and the mercury switch 25 will bemoved to closed circuit position to energize the solenoid valve 29 andper mit a flow of liquid refrigerant to the evaporator H. In addition,the crank arm 23 of the proportioning'motor 28 causes a movement of thetwo slider arms 30 and 3| with respect to the resistances 32 and 33. Thefunction of these two slider arms and their resistances in the controlsystemrwill'be described in detail later on.

The evaporators in the various spaces are supplied with liquidrefrigerant by means of three compressors indicated at 35, 36 and 31.The hot compressed refrigerant is delivered to condensers 38, 39 and 40by means of conduits 4|, 42 and 43 respectively, and a common conduit 45conducts the condenser refrigerant to the receiver 44. Supply line 41which is connected to the receiver 44 is provided with two main branches48 and 49, branch 49 feeding the evaporators in spaces A, E and F, andbranch 48 feeding the evaporators in spaces B, C and D. The evaporatorsin spaces E and F are connected to the supply branch 49 by means ofconduits 5D and 5| respectively,'and the'evaporators in spaces C and Dare connected to the supply branch 48 by means of conduits 52 and 53respectively. The expanded refrigerant from the evaporators in thespaces B, C and D flows into a branch suction line 55, the evaporator inspace B connecting directly with this branch and the'evaporators in Cand D connecting therewith by means of the conduits 56 and 51respectively. The expanded refrigerant from the evaporator in space Afeeds directly into the branch suction line 58 and refrigerant from theevaporators in spaces E and F connect therewith by means of the conduits59 and 68 respectively. The two branch suction lines 55 and 58 connectwith the main suction line6l which feeds directly into the compressorand into the compressors 36 and 31 by means of the suction lines62 and63 respectively.

It will thus be seen that the three compressors and the six evaporatorsare all connected together to form a common direct expansion systemhaving a common receiver 44 and common supply and suction lines 41 and6|. Moreover, the, evaporator in each of the spaces is provided with asolenoid valve such as the valve 29 in space D-for stopping the flow 'ofrefrigerant to the outlet of the evaporator.

The three compressors 35, 36 and 37 are controlled respectively by meansof the mercury switches 68, 69 and). Also, each of the compressors isprovided with a usual form of safety device which deenergizes thecompressor upon an abnormally highdischarge pressure or an abnormallylow suction pressure indicating an improper operation of the system.These safety devices 'are indicated at H, 12, and "I3 and are inthe-form of switches. 88, 69 and T0 are controlled respectively by meansof the cams l5, l6 and 11 which are rotated by the proportioningmotor18.As shown in Figure 1, the mercury switches are all in open circuitposition and therefore, each of the compressors is'deenergized. Upon arotation of the shaft; indicated by the dotted lines 19; in a clockwisedirection, the low side of the cam 15 will be brought adjacent'themercury switch 68 which will then move to closed circuit position. ThisWill'establish an energizing circuit for'the compressor 35 from-one linewire 88 through conductor 8|, mercury switch 88, conductor '82, switch1|, conductor 83, compressor 35, andconductor 84 back to the other linewire 85. Further rotation of the shaft 19 in a clockwise direction willcause the low side of the cam 16 to be brought oppositethe'mercury'switch 69 and permit it to move to closed circuit position.Closure of switch 99 will energize the compressor 36 by ajcircuitsimilar to'the one traced in connection with compressor 35. A furtherrotation of the shaft 19 in a clockwise direction will cause the lowside ofcam 11 to be positioned adjacent the mercury switch 10 and thisswitch will then move to closed circuit position and energize thecompressor 31 in the same manner that the other switches energizedthecompressors. 35 and 3 6. It will therefore. be seen that one, two, threeor none-of the compressors will be energized depending upon the positionof the shaft 19.

The proportioning motor 18 is provided with a control potentiometerindicated generally at 90 and a follow-up or rebalancing potentiometerindicated at 9|. The operation of proportion-- ing motors of the followup type are old and well known in the art and may take the form of theproportioning motor system shown in the Taylor patent, 2,028,110,referred to above. The electrical.proportioning system for the motor I8may be exactly like that'shown in the Taylor patent with the exceptionof the manner in which the amount of resistance in each side of thecontrol potentiometer 99 is varied. In order to effect rotation of themotor 18 the resistance present in the control potentiometer 90 betweenthe common wire 92 and the wires 93 and 94 must be varied. It iscustomary to accomplish this by connecting the common wire 92 to aslider arm which slidesover the control potentiometer, 90 to therebyvary the amount of resistance in each side. In the present system,however, each side of the control potentiometer is tapped-at variouspoints and these points are connected to resistance elements such as theelements 32 and 33 shown in space D so that when these resistf ancej'ele'ments'are cut in'iorcut out of theshunt The mercuryswitchescircuit the effective resistances of the two sides of thepotentiometer coil are varied. For example, the right hand end of theresistance 33 is connected by conductors 96 and 91 to the tap 98 in theright hand side of the control potentiometer 90. The slider 3| whichcooperates with resistance 33 is connected by means of conductors 99 andI to the tap ml in the right hand side of the control potentiometer 99.The resistance between these two taps has been designated as (1. Thus,it will be seen that the resistance 33 is electrically connected inparallel with portion d of the control potentiometer resistance whichlies between the two taps98 and NH. Thus, with the slider arm 3| on theleft hand side of the resistance 33 the effective resistance of portion11 of potentiometer 90 between the taps 98 and NH depends upon the valueof resistance of that portion of the potentiometer coil and theresistance 33, connected in parallel, However, as the slider 3| movestowards the right on resistance 33 the resistance of the shunt path isdecreased and therefore, the effective resistance of the right handportion of thepotentiometer 90 is correspondingly decreased.

The left hand end of resistance 32 is connected by conductors I93 andI04 to the tap I05 on the left hand side of the control potentiometer 90and the slider arm 39which cooperates with this resistance is connectedby conductors Hi6 and I01 to the tap I98 on the left hand side of thecontrol potentiometer. That portion of the control potentiometer betweenthese two taps has been indicated as d and is of the same size as d onthe right hand side of the control potentiometer. It will be noted thatthe resistance 32 is connected in shunt with d on the left hand side ofthe control potentiometer in the same manner that the resistance 33 isconnected in shunt with d on theright hand side of the potentiometer. Asthe proportioning motor 2|) in the space D rotates the crank arm 23 in acounterclockwise direction, the slider arms 30 and 3| will besimultaneously moved across their respective resistances 32 and 33. Suchmovement will cause the slider arm 3| to gradually cut in the resistance33 at the same time as theslider arm. 39 cuts out the resistance 32. Inother words, the slider arm 3! is increasing the resistance in the shuntpath around the portion d on the right hand side of the controlpotentiometer, whereas the slider arm 39 is decreasing the resistance ofthe shunt path around the portion d in the left hand side of thepotentiometer. This has the effect, therefore, of increasing theresistance of the right hand portion of the control potentiometer anddecreasing the resistance of the left hand portion, or in other words,has the same efiect as if a slider connected to the common wire 92 weremoving to the left across the control potentiometer 90.

Similarly, the control unit Na in space A is adapted to variably controlshunt circuits around the portion a on the right hand and a on the lefthand half of the control potentiometer 90. Control ||b variably controlsshunt circuits around portions 1) and I), control unit No variablycontrols shunt circuits around portions 0 and 0', control unit ||evariably controls shunt circuits around portions e and c, and controlunit H variably controls shunt circuits around portions 1 and f. Theeffect of all of these circuits is to vary the efiective resistancebetween the common wire 92 and the two outside wires ing theproportioning motor [8 in accordance withrthe total demand for coolingas measured by. the temperatures in each of the spaces. In order thatthe proportioning motor l8 maybe properly positioned it operates theusual follow up slider arm ||0 through a gear reduction, not shown. Theslider ||9 cooperates with the rebalancing resistance 9| and iselectrically connected to the common wire 92 by means of conductor Thus,the proportioning system for the motor 18 is similar in all respects tothat shown in the above mentioned Taylor patent, 2,028,110, with theexception of the specific manner in which the effective resistance ofthe control potentiometer 90 is varied.

The main purpose of this control system is to vary the capacity inaccordance with the demand for cooling. However, it is desired that allof the compressors should remain inoperative until the demand forcooling reaches at least a certain percentage of the total demand. vThepurpose for this is that if one of the compressors were ener-' gizedwhen the demand for cooling were extremely low, then the capacity wouldbe far in excess of that required, with the result that the compressorwould produce a very low suction pressure and the evaporator coil orcoils which were in operation would be at a very low temperature so thatnot only would the system be operating inefliciently but the very lowtemperatur in the evaporator coil would cause undesirabledehumidification of the air in the spaces in which these coils werelocated and a resultant drying out of the material therein. For thisreason the control circuits are so set up that the thermostats in thevarious spaces will indicate a demand of approximately 25% of the totalmaximum load before the proportioning motor 18 will have moved-farenough to cause closure of the mercury switch 93.

Considering the operation of. the systemas a Whole when the temperaturein each of the spaces is sufficiently low all of the thermostaticallyloperated sliders corresponding to the slider 2| in 93 and 94 for thepurpose of variably positionspace D will have moved to the right handend of their resistances 22, the splitter dampers |9 will all beJoy-passing all of the air around the evaporator IT and the sliders 39and 3| will be moved to the right hand end of their respective resist:ances. The mercury switches 25 will all be in open circuit position atwhich time the solenoid valves 29 will be closed, thereby preventing theflow of refrigerant to the evaporators H. In view of the fact that thesliders 39 and 3| are at the rig-ht hand end of their resistances all ofthe resistance between the common wire 92 and the wire 93 will have beenshunted whereas all of the resistance between the common wire 92 andwire 94 will be effective along with the relatively large amount ofresistance in parallel therewith. In other words, the resistance betweenthe common wire 92 and wire 93 will be substantially zero whereas therewill be a relatively large resistance between the common wire 92 and thewire 94. Under these circumstances the proportioning motor 18 will haverotated to a position where the slider I I9 will be at the right handend of the rebalancing resistance 9| at which time the mercury switches'68, 69 and 19 will .be supported by the high portion of the cam 15,1'6, and 11 and all of these switches will therefore be in openv circuitposition. Thus, the entire system will be deenergized when all of thespaces are sufficiently cool.

If the temperature in on of the spaces, space D for example, shouldincrease then the slider 2| will start to move to the left over theresistance 22 and cause a corresponding movement of proportioning motor20. Motor 28 will cause a counter-clockwise rotation of the crank arm 23thereby causing the splitter damper I9 to permit a slight amount of airto flow across the evaporator l'l. Movement of the crank arm 23 willalso close mercury switch 25 to open the valve 29 to permit flow ofrefrigerant to the evaporator [1. Also the movement of the crank arm 23will cause a movement of the slider arms 38 and 3i toward the left whichwill in effect add resistance to the potentiometer 90 between the taps93 and IUI and decrease the resistance between the taps I05 and I08.This in efiect, adds resistance between the common wire 92 and the wire93 and removes resistance between the common wire 52 and the wire 94.Thus, the electrical system becomes unbalance-d and the proportioningmotor 18 rotates in a direction to cause the slider arm III] to movetoward the left to remove resistance between the wires 92 and 93 and addresistance between the wires 82 and 94. When the system has beenrebalanced by the slider arm l I!) the proportioning motor 13 will stop.

It will be noted that the siZe of the sections a, b, c, d, e, and f, anda, b, c, d", e, and f of the control potentiometer 9i) bear a directrelationship to the percent of total load which the corresponding spacesrepresent. Thus, space A represents of the total load on the entiresystem and therefore, the two portions a and a on the controlpotentiometer comprise 20% of the total potentiometer resistance.Likewise, space B represents 15% of the total load on the system and thetwo portions b and b represent 15% of the total control potentiometer,etc. Thus, even though the temperature in the space D reaches a maximumvalue, the demand for cooling would still be only 15% of the maximumcooling demand possible, assuming of course that all of the other spaceswere satisfied. Th cam 15 controlled by the proportioning motor 18 hasbeen so set on the shaft 19 that the mercury switch 68 will not beclosed until there is at least a demand for cooling and therefore, thespace D by itself is incapable of causing operation of any of thecompressors. However, in the normal operation of the system it is Veryunlikely that one space will be calling for a maximum amount of coolingwhile the same time all of the other spaces remain satisfied. It will beclear, therefore, that the temperature in each space will have its ownindividual effect upon the effective resistances in each side of thecontrol potentiometer with the result that the proportioning motor 73will be positioned in accordance with the total demand for cooling asindicated by the temperature in all of the spaces.

As soon as the total demand for cooling reaches 25% the proportioningmotor 78 will have rotated far enough for the T5 to permit closing ofthe mercury switch $3, and this switch will enersize the compressor bymeans of the circuit traced above. In order to prevent short cycling ofthe compressor, the mercury switch 68 has been provided with a slighthump in the middle of the tub in order that it will have a slightdifferential so that the demand for cooling will have to decreaseapproximately 5% before the motor is will have rotated in a reversedirection far enough to cause opening of the mercury switch 58. In otherwords, the mercury switch 68 will close upon a 25% demand for coolingand will reopen when this demand has been reduced to approximately 20%.It will be clear that as the demand for cooling increases theproportioning motor '58 will be rotated farther and farther until, whenthe demand reaches approximately 50%, the mercury switch E9 will beclosed and the compressor 36 energized. If the operation of the twocompressors is still insuflicient to maintain the proper temperaturewithin the spaces then the temperatur therein will continue to rise andthe propcrtioning motor '18 will be rotated until the cam ll permitsclosing of the mercury switch ii! at which time the compressor 37 willbe energized. fhe system will now be operating at maximum capacity. Itwill b clear, of course, that when the temperatures in the variousspaces begin to fall, the reverse operation will take place with thecompressor 37 being deenergized first, then the compressor 35, andfinally when the demand falls to 20% of maximum demand the compressor 35will be deenergized.

In some instances it may be desirable to substitute a direct on and offcontrol for the proportioning control in the various spaces. In otherwords, it may be desirable to shunt each of the various portions a to fand a to j of the control potentiometer 9G in one step by means of aswitch or to entirely [break the shunt circuit around these portions. Ifsuch an operation is desirable then a control instrument such as the onedisclosed at 550 in Figure 2 may be used. This instrument comprises atemperature responsive bellows i5l which is adapted to rotate a pair ofmercury switches i512 and l in a counter-clockwise direction upon anincrease in temperature. The mercury switch N52 is a double-ended switchwith the electrodes in the right hand end of the switch being bridgedwhen the temperature in the space is below a predetermined value, andthe electrodes in the left hand end of the switch being bridged when thetemperature is above such predetermined value. The electrodes in theright hand end of the switch may be connected directly to conductors 9i;and 95 shown in space D in Fig. 1 at which time the portion 0! in thright hand half of the control potentiometer will be shunted. Theelectrodes in the left hand end of the switch may be connected directlyto conductors IE3 and IE6 also shown in space D in Figure 1 by which areconnected across portion 11' in the left hand end of the controlpotentiometer 8i With the bellows E5! in the position shown in Figure 2th shunt across portion d in the left hand side of the controlpotentiometer will be open so that the resistance between the taps H35and I68 will be completely effective. Upon an increase in temperaturethe mercury switch E52 will rotate in a counterclockwise direction tocause unbridging of the conductors 96 and 99 and the bridging of theconductors H33 and I68. This will in effect cut the resistance ofportion (1 out of the left hand side of the control potentiometer andinsert it into the right hand portion of the potentiometer. In otherwords, the control device of Figure 2 accomplishes in one step what thecontrol de vice of Figure 1 with its slider arms 3K3 and BI accomplishgradually upon changes in temperature. The mercury switch I53 shown inPicture 2 controls the circuit to the solenoid valve 29 and hence.performs the same function as the mercury switch 25 shown in space D ofFigure 1.

It is possible for all of the spaces to be provided with a controldevice as shown in Figur 2.

or if desired, some of them may be provided with static switchesindicated at 204, 205 and 206, I

each of which is intended to be located in a separate space in whichevaporators are located which are intended to be fed with liquidrefrigerant by the compressors 202 and 203 in the same mannerasdisc'losed in Figure l.

frigerant to the evaporatorin the space in which the thermostatic switch204 is located, thesolenoid valve 200 is adaptedto control the flow ofrefrigerant to the evaporator in the space in which the thermostaticswitch205 is located-and the solenoid valve 209 is adapted to controlthe flow of refrigerant to the evaporatorin the space in which thethermostatic switch 206 is located.

The thermostatic switches 204,205 and 206 are identical and therefore,only 204 will be described in detail. The thermostatic switch 204comprises a bellows 212 which is adapted to operate the two mercuryswitches 213 and 214. The bellows 2121s a thermostatic bellowsresponsive to the temperature in the space and is shown in the positionwhich it will occupy when the temperature in the space is at or belowthe desired value, at which time the two mercury switches 213 and 214are in open circuit position. Upon an increase in temperature in thespace in which the bellows 212 is located, the bellows will expand andwhen the temperature increases above the desired value it will rotatethe mercury switches The solenoid valve 201 is adapted to control thehow of re- 1 in a counter-clockwise direction, thereby moving I linewire 220. This will result in the energization of the solenoid valve 201at which time it will permit the flow of refrigerant to the evaporatorwithin the space, providing liquid refrigerant is available at the time.The mercury switch 213 will be closed at the same time as the switch 214and a second circuit will be established from the line wire 215 throughconductors 216, 222, mercury switch 213, conductors 223 and 224,resistance element 225, conductor 226, current responsive relay 200 andconductor 221 back to the other line wire 220. A parallel circuit willbe established from the conductor 223 through conductor 228, resistanceelement 229, conductor 280, relay 201 and conductor 231 to the line wire220.

The thermostatic switch 205 is also provided with a pair of mercuryswitches such as those disclosed in the thermostatic switch 204 and whenthe temperature in the space in which the thermcstatic switch 205 islocated rises above adesired value, a circuit is established from theline wire 216 through conductor 2.35, thermostaticswitch 205, conductor236, solenoid valve208and con? ductor 231 back to line wire 2 20. Anadditional and 239 and through resistance element 240'to conductor 226and then through the relay 200 and conductor 221 to. the line wire 220.A parallel circuit extends from the conductor 238 through conductor 241,resistance, element 242, conductor 260, relay 201, and conductor 231 tocircuit is likewise closed through conductors'238 wire 220; Likewise,the thermostatic switch 206, whichf is'locatedjinfthe third space, isadapted tofie's'tablishfafcircuit.'from"the line wire 215 "throughconductor 245, conductor 246, solenoid valve 200'and conductor-241 toline wire. 220. At thesame time a circuit is. set up from line wire"2"1'5,""conductor2'45, thermostatic switch 206, throughconductor 250,conductor 251, resistance feiemenmsz t0 conductor 226,relay 200 andconductor 22 1-back to line wire 220. A'parallel circuitextends-fromconductor 250 through conductor 253an'd resistance element254, conductor 230, relay'201 and conductor 231 back to the line wire220.

, As in the system shown in Figure 1, the various thermostatic switches204, 205 and 206 may be locatedin spaces which represent different loadsupon, the system. Thus, the space in which the thermostatic switch 204is located may represent a relatively small percentage of the totalload,

thespace inwhich the thermostatic switch 205 is located may representalarger percentage, and the space in; which the thermostatic switch 206is located may represent an even larger percentage. v

It may not be desirable to. energize either of the compressors in theevent that the thermostatic switch 204 is the only one calling forcooling-Therefo e. if this switch is moved to closed position-the;solenoid valve 201 is'opened and a circuit is established through theresistance element 225 and through the relay 200 and also through theresistance 229 and relay 201. The two resistanceelements 225 and 229 arerelatively large and therefore, may permit only a relatively smallamount of current to flow through the relays 200 and 20 1. The relaysare biased to open circuit positionby the biasing springs 260 and 261and these springsprevent the relays from pulling in their armatures' 262and 263 respectively when the only current flowing through the relaysisthat which passes through the resistance elements 225 and 229. Thus,when the thermostatic switch 2041s the onlyone' calling for cooling,neither of the compressorsis energized,

Similarly, if the thermostatic switch 205 is the only one which iscalling for coolingyall of the current which passes through the relay200 must pass through the resistance element 240 and all of ;the'current which passes through the relay 201 must pass, through theresistance element 242. Here again, thebiasing spring 260 and 261 may beso selected that they will prevent either "of the'relaysfrom pulling inat this current value,

and therefore, neitherof the compressors is energized. However, whenonly the thermostatic switch 206 iscalling for cooling, the current flowthrough the relay 200 passes through the relatiyel-ysmall resistance252, and likewise, the currentpassing through the relay 201 passesthrough thesmall resistance 264. The biasing spring 260 is; so chosenthat the current flow through the resistance 252 is 'sufiiciently largeto cause the relay 200 to pull in its armature 262 thereby establishinga circuit from the line wire 215 through conductor 265, armature 262,conductor 266, compressor 202 and conductor 261 backto the other linewire 220. Thus, the thermostatic switch 206 is capable of energizing thecompressor 202 upon a call for cooling. It will be noted, however, thatthe resistance 254 is larger than the resistance 252, and is in fact, solarge that the current flow through the'relay 201 is insufliclentto'cause it to pull in its armature. Therefore the compressor 203remains deenergized at this time. If the thermostatic switch 205 shouldcall for'co'oling at this time a circuit is setup through the resistance242 andthis current added to the priority flowing through the relay 20lis sufficient to cause this relay to.pu1l in its armature 263 at whichtime the compressor 203 is energized from a, circuit extending frorn theline wire 2l5 to co'nductor258, armature 263, conductor 269, compressor203, and conductor 210 back to the other line'wire 220. The system istherefore now operating at maximum capacity even though the thermostaticswitch 204 is still satisfied.

Preferahlythe resistances and relays are so chosen in this'embodiment ofmy invention that neither the thermostatic switch 204 nor 205 alone canstart either ofthe compressors. The thermostatic switch 205, however,alone is operative to'start the compressor 202 but not the compressor203. I f'bo th the thermostatic switches EMand 2E5Qare"ca1ling forcooling they can start the compressor 202 but not the compressor 263'.However, if the thermostatic switches 205' and 205 together call forcooling,

they can start both the compressors but the thermostatic switches 205and 204 together can only start the compressor 202.

The above relationshipis given for purposes oi illustration only. It isobvious that more compressorsmay be.' used and also that thesecompressors'mayoperate to cool any number of spaces, eachspace having anindividual thermostatic switch and controlling the flow of current toresistances which are inversely proportional to the load on the systemwhich that particular space represents. In other words, the smaller theload represented by the space, the larger the resistance controlledthereby, and hence the smaller the value of current which will bepermitted to fiow to the relay." It will also be obvious to thoseskilled intheart, that a thermostat operating a variable resistance maybe substituted for the bellows 2 l2 and mercury switch N3 in any or allof the spaces. This would'give a more or less graduating control of thecurrent flow through the relays 20L and would perhaps give a moreaccurate indication ,of the total load on the systemthan the mercuryswitch arrangement as disclosed.

Many other changes and modifications of the above system willundoubtedly occur to those who are skilled in the 'art, and it istherefore my intention to be limited only by, the scope of the appendedclaims and not by the specific em,- bodiments of this invention whichhas been disclosed herein.

I'claim as my invention:

1 1. In anair conditioning system for a pluralityof spaces representingunequal loads on 'said system, in combination, evaporator means for eachspace, variable capacity compressor means for supplying liquidrefrigerant to said evaporator means, a variable position control'de'vi'ce for varying the capacity of said compressor'means, saidcompressor means being inoperative as said control device moves from afirst position to an intermediate position at which time said compressormeans operates at minimum capacity, said capacity being increasedas saidcontrol device moves from said intermediate position to a finalposition, a tern 'perature responsive device in each of said spaces, andconnections by means of which each tem- 'perature responsive. devicemoves said control device an amount dependent both upon the percentageof the total load on the system which that particular space representsand the amount the temperature in such space has deviated from thetemperature it is desired to maintain therein.

,2. In an air conditioning system for a plurality of spaces representingunequal loads on said system, in combination, evaporator means for eachspace, variable capacity compressor means for supplying liquidrefrigerant to said evaporator means, a temperature responsive device ineach of said spaces, electric circuit means, means operated by eachtemperature responsive device for changing a condition of said circuitmeans an amount dependent both upon the load represented by the space inwhich that particular temperature responsive device is located and inaccordance with the amount the temperature in said space has deviatedfrom the desired value, and means responsive to the condition of saidelectric circuit means for rendering said compressor means operative atminimum capacity when the condition of said circuit indicates asufficient demand to warrant such operation, and for increasing saidcapacity upon an increase in said demand.

3. In an air conditioning system for a plurality of spaces representingunequal loads on said system, in combination, evaporator means for eachspace, variable capacity compressor means for supplying liquidrefrigerant to said evaporator means, temperature responsive device ineach of said spaces, electric circuit means, means operated by eachtemperature responsive device for changing a condition of said circuitmeans an amount dependent upon the load represented by the space inwhich that particular temperature responsive device is located, andmeans responsive to the condition of said electric circuit means forrendering said compressor means operative at minimum capacity when thecondition of said circuit indicates a sufiicient demand to warrant suchoperation and for increasing said capacity upon an increase in saiddemand, at least one of said spaces representing such a small load thatits temperature responsive device is incapable of changing the conditionof said circuit means sufliciently to cause operation of said compressorif no other space is demanding such operation.

4. In an air conditioning system for a plu- 'rality of spaces, incombination, evaporator means for each space, variable capacitycompressor means for supplying liquid refrigerant to said evaporatormeans. a temperature responsive device in each of said spaces, electriccircuit means, proportioning means operated by each temperatureresponsive device for varying a condition of ,said circuit means inproportion to the deviation in temperature in each space, and meansresponsive to the condition of said electric circuit means for renderingsaid compressor means operative at minimum capacity when the conditionof said circuit indicates a suflicient demand to warrant such operation,and for increasing said capacity upon an increase in said demand.

5. In an air conditioning system for a plurality'of spaces representingunequal loads on said system, in combination, evaporator means for eachspace, variable capacity compressor means tor supplying liquidrefrigerant to said evaporator means, a temperature responsive device ineach of said spaces, electric circuit means, means operated by eachtemperature responsive device for changing the value-of current flowingthrough said circuit means, the effect of said current changing meansupon the current in said circuit means being dependent upon the loadrepresented by the space in which the corresponding temperatureresponsive device is located, a plurality of relays each requiring adifierent current value to operatively energize the same in control ofsaid variable capacity compressor means, a first of said relaysresponding to a first value of current in said electric current means torender said compressor means operative at minimum capacity, said firstcurrent value corresponding to a suflicient demand to warrant compressoroperation, the remainder of said relays responding to an increase insaid current value to increase the capacity of said compressor means.

6. In an air conditioning system for a plurality of spaces representingunequal loads on said system, in combination, evaporator means for eachspace, variable capacity compressor means for supplying liquidrefrigerant to said evaporator means, a thermostatic switch for eachspace, a plurality of current responsive relays for controlling saidcompressor means, and separate resistance means in series with each ofsaid thermostatic switches and each of said current responsive relays,said resistance means being of such a size that the closure of anythermostatic switch will cause an increase in current through saidrelays, said current increase being proportional to the load representedby the space to which that particular thermostatic switch corresponds, afirst of said relays responding to a first value of current to rendersaid compressor means operative at minimum capacity, said first currentvalue corresponding to a suflicient demand to warrant compressoroperation, the remainder of said relays responding to an increase insaid current value to increase the capacity of said compressor means.

'7. In an air conditioning system for a plurality of spaces representingunequal loads on said system, in combination, evaporator means for eachspace, variable capacity compressor means for supplying liquidrefrigerant to said evaporator means, an electrically operable devicefor varying the capacity of said compressor means, means including anelectrical balancing system for positioning said device, said electricalbalancing system having a control potentiometer for unbalancing the sameand a rebalancing potentiometer for rebalancing the same, the thermostatresponsive to the temperature in each of said spaces, resistance meansfor each thermostat, each thermostat varying said resistance means inaccordance with the space temperature to which it responds, each of saidresistance means being connected in shunt with a portion of said controlpotentiometer, said portion being proportional in size to the loadrepresented by the corresponding space, driving connections between saidrebalancing potentiometer and. said device whereby said device ispositioned in accordance with the load on the entire system asdetermined by said thermostats, means operated by said device forpreventing operation of said compressor means until the demand foroperation is such as to correspond substantially to the minimum capacityof said compressor means, and means operated by said device forincreasing said capacity upon an increase in the demand.

8. In an air conditioning system for a plurality of spaces representingunequal loads on said system, in combination, evaporator means for eachspace, variable capacity compressor means for supplying liquidrefrigerant to said evaporator means, an electrically operable devicefor varying the capacity of said compressor means, means including anelectrical balancing system for positioning said device, said electricalbalancing system having a control potentiometer for unbalancing the sameand a rebalancing potentiometer for rebalancing the same, thermostatsresponsive to the temperature in each of said spaces, resistance meansfor each thermostat, each thermostat varying said resistance means inaccordance with the space temperature to which it responds, each of saidresistance means being connected in shunt with a portion of said controlpotentiometer, said portion being proportional in size to the loadrepresented by the corresponding space, driving connections between saidrebalancing potentiometer and said device whereby said device ispositioned in accordance with the load on the entire system asdetermined by said thermostats, means operated by said device forpreventing operation of said compressor means until the demand foroperation is such as to correspond substantially to the minimum capacityof said compressor means, means operated by said device for increasingsaid capacity upon an increase in the demand, and means operated by eachthermostat for varying the efiect of the evaporator on the air in thespace to whose temperature said thermostat responds.

9. In an air conditioning system for a plurality of spaces, incombination, evaporator means for each space, variable capacitycompressor means for supplying liquid refrigerant to said evaporatormeans, valve means for controlling the flow of refrigerant to each ofsaid evaporator means, means for varying the effectiveness of each ofsaid evaporator means, means responsive to the temperature in each ofsaid spaces, means operated by each temperature responsive means foropening its associated valve means upon an initial rise in temperatureand for operating its associated effectiveness varying means to increasethe effectiveness of its associated evaporator as the temperaturecontinues to rise, and means operated by all said temperature responsivemeans to control the capacity of said variable compressor means toincrease the capacity thereof as the total demand by all saidtemperature responsive means increases.

10. In an air conditioning system for a plurality of spaces representingunequal load on said system, in combination, evaporator means for eachspace, variable capacity compressor means for supplying liquidrefrigerant to said evaporator means, a temperature responsive device ineach of said spaces, electric circuit means, means operated by eachtemperature responsive device for changing a condition of said circuitmeans an amount dependent upon the load represented by the space inwhich that particular temperature responsive device is located, andmeans responsive to the condition of said electric circuit means forrendering said compressor means operative at minimum capacity when thecondition of said circuit indicates a sufiicient demand to warrant suchoperation and for increasing said capacity upon an increase in saiddemand, at least one of said spaces representing such a small load thatits maximum demand, as determined by a full range of movement of itstemperature responsive device, is less than said sufficient demand whichis required to start a compressor.

ALWIN B. NEWTON.

